The present invention relates in general to drug delivery systems, and, in particular, to a new and useful apparatus and method for the delivery of a drug to a subject through a needle.
Published U.S. Patent Application US 2006/0122555 entitled Drug Infusion Device . . . , is incorporated here by reference and is owned by the assignee of the subject application, Milestone Scientific Inc., and is invented by the current inventor. This application is not prior art to the subject application but discloses an actuator with a mechanism for sensing and for feeding back the reaction force being experienced by a shaft being displaced by the actuator, for regulating activation of the actuator in response to the reaction force.
U.S. Published Patent Application 2004/0215080 to Lechner is incorporated here by reference for its teaching of a device for locating an anatomical cavity in the body. This reference is interesting for its use of a continuous audible signal that indicates the pressure of a fluid in a reservoir that is meant to be injected into the body of a subject through a needle. When the sought cavity has been reached by the needle, the audible signal indicates a corresponding pressure drop in the reservoir to the operator. Fluid pressure in the reservoir and not at the needle point is measured and used in this published patent application. There is no teaching or suggestion of the correlation between tissue type and a minimum or desired threshold pressure, nor the importance of taking or calculating the needle tip pressure.
Other important differences between the Lechner application and the present invention are illustrated in paragraph [0035] of the image version of the Lechner application where it is stated that: “calibration of the pressure-measurement is not critical, since the user is working on the basis of changes which he detects in the sound signal.” Lechner uses a relative scale to determine identification of “cavity” or structure. In paragraph [0063] Lechner goes on to expand the use of the device to “locate a region” or “tumor in the body of a person” based on the observation that a tumor generally has different properties from the surrounding tissue, thus teaching the importance of a relative pressure change in which it is situated, and in particular the tumor will present a different resistance to the penetration of a fluid as compared to the surrounding tissue.
The Lechner device thus requires the detection of a relative change in pressure to differentiate and discriminate from the surroundings. It is therefore a system based on relative change, hence the need to provide a continuous acoustic feedback otherwise the user would miss the relative change. The Lechner device cannot identify any specific tissue based on absolute value of pressure, but can only differentiate when there is a substantial change in a relative pressure.
U.S. Pat. No. 6,200,289 which was co-invented by the inventor of the subject application, its related U.S. Pat. Nos. 6,786,885; 6,945,954; and 6,887,216; as well as its related U.S. Published Patent Applications 2005/0004514; 2006/0102174; and 2006/0122555, which are all incorporated here by reference, disclose and claim devices that control the exit pressure for a fluid being injected into a patient.
A handpiece and system marketed by the assignee of the subject application under the registered trademark THE WAND, can be used to administer drugs in general, and dental anesthetic in particular. This handpiece and other aspects of the overall system for administering anesthetics in a controlled manner with reduced pain to the subject, are disclosed and claimed in U.S. Pat. Nos. 4,747,824; 5,180,371; D422,361; D423,665; D427,314; 6,132,414; 6,152,734; and 6,652,482; which are also all incorporated here by reference.
U.S. Pat. No. 6,296,623 discloses a needle handle and anesthetic carrier assembly for delivering anesthetic under pressure to a patient and U.S. Pat. No. 6,629,958 discloses a hypodermic needle structure which can be used, for example, for administering a periodontic ligament (PDL) injection, which is also referred to as an intraligamentary injection.
The PDL is where the gingival tissue meets the tooth across a thin band of ligament that connects the tooth to the bone. This injection, however, is notoriously difficult to administer properly and is often painful to the patient due to various factors, including the extreme hardness or high-density of PDL tissue.
The periodontal ligament injection technique was first described in the early 1900's by Doctors Guido Fischer and Cassamani. The technique utilized a standard dental syringe and a “blind” placement of the hollow-bore metal needle into the gingival sulcus, and advancing the needle into the periodontal ligament located between the root surface (cementum) and the bony socket of a tooth. Once the needle was in the periodontal ligament, the clinician generated maximum pressure on the standard dental syringe or on a high-pressure pistol-grip lever syringe. The total recommended volume of anesthetic solution was 0.2 ml to 0.4 ml using this method.
Critical to the technique was the placement of the needle tip within or at the entrance to the periodontal ligament as well as the generation of high pressure or typically between 600-1200 psi to drive anesthesia into this dense tissue. Both of these features of the technique have significant pitfalls. Authors over the past century have described the difficulties of proper needle position within the desired location because of the obvious lack of direct visualization and identifiable anatomic landmarks, hence a “blind” approach to needle placement. In addition to placement of the needle tip, maintaining correct placement during administration is difficult to achieve and to confirm.
Applying maximum hand-pressure on the dental syringe generates extreme high pressures. Although advocated to forcibly move anesthetic solution through the dense tissues, unusually high syringe pressures cause tissue damage as evidenced by histologic, animal and human studies that have repeatedly demonstrated the adverse tissue reactions from the use of such high pressures. This tissue damage results in subjective pain perception reported by dental patients when the intraligamentary or PDL injection is performed using a traditional technique and mechanical dental syringe.
In addition to the needle placement issues and problems with high pressure in tissues, traditional syringes do not allow the clinician to confirm that the correct amount of anesthesia has been delivered, as both blockage and/or leakage during injection can occur. Due to these difficulties, the previous technique can lead to insufficient duration of anesthesia. Workers in the field have reported a 10 to 20 minute duration of effective pulpal anesthesia for the PDL technique that they tested. Their research used a variety of local anesthetics with varying concentrations of vasoconstrictors. When performed with greater volume, the PDL technique demonstrated a longer effective working time correlated with a larger dosage administered. Limited anesthetic solution volumes result in limited duration of anesthesia.
These traditional techniques and technologies utilized in routine intraligamentary injections, are thus hampered by the blind nature of the injection, the extreme pressures generated in local tissues during the procedure, and the relatively small volume of anesthesia that is reliably delivered. These factors have resulted in a reduced duration of anesthesia and increased pain associated with tissue damage.
A need exists for an improved apparatus and method for injecting a drug into selected tissues of a subject with increased control and, importantly, increased feedback information to the practitioner who is administering the injection.